This invention relates to a method of operating and to a control system for the fuel system of a compression ignition engine the fuel system including control means operable by the control system to determine the amount of fuel supplied to the combustion chambers of an associated engine.
In a known fuel system individual engine actuated fuel pumps supply fuel to respective engine cylinders and each fuel pump includes a control valve operable to determine the amount of fuel supplied to the respective engine cylinder. In another known fuel system a single pump is provided and the fuel delivered by the pump is supplied to the engine cylinders in turn by means of a fuel distributor. A single control valve is utilized to determine the amount of fuel supplied to the engine cylinders.
During the operation of an engine there is a natural fluctuation in the speed of the engine as each cylinder partakes of its power stroke. If the engine is in good condition and each cylinder is receiving the same amount of fuel the fluctuations in the speed should be equal. If however one cylinder receives more or less fuel than the remaining cylinders due to some defect in the fuel system or if one cylinder is defective because of leakage past the valves or piston rings then the fluctuation of speed will not be the same.
The equalization of fuel flow can be effected by modifying the operation of the control valve for the particular pump associated with the cylinder which is receiving more or less fuel, or by modifying the operation of the single control valve during the time when it is dealing with the supply of fuel to the cylinder which is receiving more or less fuel. Supplying more fuel to a defective cylinder may reduce the fluctuation of speed but it is desirable that some sort of warning should be given when the degree or rate of modification to the operation of the control valve exceeds a predetermined amount.
With a four cylinder engine it is possible to measure during operation of the engine, the engine speed during each power stroke and to compare this speed with the average speed or to compare it with the speed measured during the previous power stroke. In this way it is possible to identify which cylinder is at fault, GB No. 2112180 and GB No. 2196153 described systems of the aforesaid type.
When the engine has an increased number of cylinders the natural fluctuation of engine speed is reduced and whilst in theory it should be possible to use the techniques advanced in the aforesaid specifications to identify the defective cylinder, in practice, it is difficult to achieve a satisfactory result.